Hydrocarbons, such as fossil fuels, refined petroleum products, etc., for example, natural gas, liquefied natural gas, sour gas, crude oil, naphtha, heavy aromatic naphtha, gasoline, kerosene, diesel oil, light oil, heavy oil, FCC slurry, asphalt, oil field concentrates, etc., often contain sulfur-containing compounds, such as hydrogen sulfide or a variety of —SH group-containing compounds (typically various mercaptans), etc. Toxicity of hydrogen sulfide is well known, and in the industry dealing with fossil fuels or refined petroleum products, in order to reduce the content of hydrogen sulfide to a safe level, considerable costs and efforts are exerted. For example, as for pipeline gas, what the content of hydrogen sulfide does not exceed 4 ppm is required as a lot of regulation values. In addition, hydrogen sulfide and a variety of —SH group-containing compounds (typically various mercaptans) tend to be released into a vapor space because of volatility thereof. In that case, their offensive odors are of a problem in storage places and/or surrounding places thereof and through pipelines and shipping systems used for transportation of the aforementioned hydrocarbons.
From the foregoing viewpoints, in large-scale facilities dealing with fossil fuels or refined petroleum products, systems for treating a hydrogen sulfide-containing hydrocarbon or hydrocarbon fluid are commonly installed. These systems include an absorption tower coming into contact with a hydrocarbon or a hydrocarbon fluid and filled with an alkanolamine, PEG, a hindered amine, etc., which absorb a sulfur-containing compound, such as hydrogen sulfide, or a variety of —SH group-containing compounds (typically various mercaptans), carbon dioxide in some case, and which are capable of being regenerated and used in the treatment system after absorption.
Meanwhile, it has been known for long that a triazine is used for removal of hydrogen sulfide in a hydrocarbon. However, there is involved such a defect that the triazine cannot be used unless used under basic conditions (the triazine is decomposed under neutral to acidic conditions).
It has also been known for long that an aldehyde compound is used for removal of hydrogen sulfide in a hydrocarbon. Specifically, PTL 1 discloses the reaction of an aldehyde compound with hydrogen sulfide, particularly the reaction of a formaldehyde aqueous solution with hydrogen sulfide in an aqueous solution at a pH ranging from 2 to 12. Since then, there have been made many reports regarding the use of an aldehyde compound for the purpose of removal of hydrogen sulfide. For example, in PTL 2, a water-soluble aldehyde, such as formaldehyde, glyoxal, glutaraldehyde, etc., is used in a form of an aqueous solution as a hydrogen sulfide removing agent in a hydrocarbon.
In the case where the hydrogen sulfide removing agent that is an aqueous solution is merely added to the hydrocarbon, an improvement is demanded from the viewpoint of mixing. For example, PTL 3 mentions that the removal efficiency of hydrogen sulfide can be improved by adding an emulsifying agent, such as sorbitan sesquiolate, to the aforementioned aldehyde. In addition, in PTL 4, in order to efficiently remove hydrogen sulfide in a heavy oil, the hydrogen sulfide removing agent that is an aqueous solution and the heavy oil are emulsified in an injection system including a static mixer.
In addition, in the case of using, as the hydrogen sulfide removing agent, the aforementioned water-soluble aldehyde in a form of an aqueous solution, there is a concern that corrosion of equipment is caused due to the presence of an organic carboxylic acid by oxidation of formaldehyde, glyoxal, or glutaraldehyde in the aqueous solution. From this viewpoint, in PTLs 5 and 6, it is proposed to jointly use, as a corrosion inhibitor, a phosphate salt, such as LiH2PO4, NaH2PO4, Na2HPO4, KH2PO4, K2HPO4, etc., a phosphate ester, a thiophosphate, a thioamine, or the like.
However, it is well known that formaldehyde is a mutagenic substance. In addition, as in the Test Examples as described later, glutaraldehyde has toxicity and is hardly decomposable, and therefore, these aldehydes involve problems regarding safety at the time of handling and influence on environment.
Meanwhile, PTL 2 discloses use of not only the aforementioned water-soluble aldehyde but also acrolein with higher organicity as the hydrogen sulfide removing agent. In SPE Annual Technical Conference and Exhibition SPE146080, held in Denver, Colo. State, U.S.A. on Oct. 30 to Nov. 2, 2011, an announcement regarding removal of hydrogen sulfide with acrolein as an active ingredient is also made. However, the acrolein has strong toxicity and is a compound whose concentration is strictly controlled from the standpoints of occupational safety and environmental safety, and therefore, there is involved such a problem that attention is required for handling.